The invention relates specifically to the field of electronic reproduction technology and relates to a method for the recognition of hues and colors in colored areas and also relates to a circuit arrangement therefore.
What is to be understood by colored areas are, for example, color originals for electronic reproduction technology, colored pattern designs for the acquisition of control data for textile processing machines, or colored print media.
Before the actual color recognition, color recognition spaces within a color space are defined with the assistance of color recognition circuits around those color locations whose colors within the colored area are to be recognized as individual colors. During the color recognition, the colored area or surface to be analyzed is trichromatically scanned point-by-point and line-by-line and color signals which represent the color coordinates of the color locations of the scanned colors in the color space are acquired by means of opto-electronic conversion of the components of the scan light. By means of evaluating the color signals in the color recognition circuit, a determination is then made with respect to which defined color recognition spaces the color locations of the scanned colors fall and these colors being thus identified.
Such color recognition circuits are employed in reproduction technology in, for example, the production of color separations by means of color scanners for polychromatic mixed printing (multicolor printing) or for single color printing.
In the production of color separations for polychromatic mixed printing, the color signals acquired by means of scanning the color original are converted into color separation signals by means of a basic color correction, the color separation signals being a measure for the intensity of the color application of the printing inks yellow, magenta, cyan, and black in the printing process.
The basic color correction eliminates color errors which result, among other things, due to the different spectral properties of original colors and printing inks and, under given conditions, the desired edited information of the reproduction is modified relative to the original. In addition to the basic color correction, an additional selective color correction is often executed, and very specific colors or hues are designationally corrected.
In selective color correction, there is then the problem of recognizing the color or hues to be specifically corrected with the assistance of color recognition circuits and of deriving selective correction signals from the color recognition signals.
When the color original to be reproduced has a color progression, i.e. differing color saturation and/or brightness within a color or hue, then selective correction signals whose intensity likewise depends on the color progression are required in order to be able to execute progressive or bled, i.e. gradually changing, color corrections.
Apart from polychromatic mixed printing, each individual color to be printed in single color printing which, for example, encompasses textile, decorative, packaging, or porcellan printing, is blended before the printing process, and the various individual colors are then transferred to the print medium in separate operations. In single or individual color printing, there is then the problem of producing a corresponding color separation with the assistance of color recognition circuits for each individual color of the color original to be inked. In this case, a color separation signal must be derived from the color recognition signal.
When it is again a matter of color originals having color progressions, the color separation signal must also be progressive, since it must supply information both with respect to the topical distribution of the inked individual color as well as with respect to the topically different intensity of the color application.
Color recognition circuits are already known from U.S. Pat. No. 3,210,552 and German LP No. 25 44 703 corresponding to U.S. Pat. No. 4,110,826, both incorporated herein by reference, wherein the color recognition spaces within the color space are bounded by means of electrical thresholds. The applicability of a scanned color to one of the bounded color recognition spaces is determined by means of a value-wise comparison to the thresholds of the color signals acquired in the scanning of the color original to be analyzed.
Another type of color recognition has been disclosed in the German OS No. 29 23 468 corresponding to U.S. Pat. No. 4,414,635, incorporated herein by reference. The color recognition circuit herein essentially comprises a color recognition memory in which every color locus of the color space has a memory location allocated to it and every memory location is addressable by the color coordinate triad of the corresponding color locus. Color numbers which identify the colors to be recognized are deposited at the memory locations, so that all of the memory locations or color loci respectively occupied by the same color number form a color recognition space. During the point-by-point and line-by-line scanning of the colored area or surface, the color signal triads thus acquired address the color recognition memory and the addressed color numbers are output, the scanned colors being thus identified.
The aforementioned color recognition circuits emit color recognition signals which merely supply a yes/no statement as to whether a scanned color falls into a defined color recognition space or not. Such color recognition signals are not suitable for generating bled or progressive correction signals and color separation signals.
A further color recognition circuit is known from the German Letters Patent No. 26 28 053, corresponding to U.S. Pat. No. 4,194,339, incorporated herein by reference. The color recognition signal of this circuit, in addition to the yes/no statement, also supplies information with respect to the three-dimensional spacing of the scanned color from a freely selectable center of gravity color within a color recognition space defined around the center of gravity color. Color variations can in fact be recognized with the assistance of this color recognition circuit, but the color recognition spaces cannot be optimally matched in terms of shape and size to the color regions given by the color progression in the color original, so that the color recognition circuit does not supply unequivocal information about the color saturation and/or brightness. The desired, bled or progressive correction signals and color separation signals can therefore likewise not be derived from the color separation signal. A further disadvantage of the known color recognition circuit is that it is not specifically designed for the definition or the recognition of hues, so that optimum selective correction signals and color separation signals cannot be derived for individual hues.